Heater



FIG. 1 is a front elevational view of a heater showing my new design;

FIG. 2 is a rear elevational view thereof;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom plan view thereof;

FIG. 5 is a side elevational view thereof;

FIG. 6 is a rear perspective view thereof;

FIG. 7 is a front perspective view thereof.

The ornamental design for a heater, as shown and described.